Through air drying has become the technology of preference for making one-ply absorbent paper for many manufacturers who build new absorbent paper machines as, on balance, through air drying (xe2x80x9cTADxe2x80x9d) offers many economic benefits as compared to the older technique of conventional wet-pressing (xe2x80x9cCWPxe2x80x9d). With through air drying, it is possible to produce a single-ply absorbent paper in the form of a tissue with good initial softness and bulk as it leaves the absorbent paper machine.
In the older wet pressing method, to produce a premium quality, absorbent paper, it has normally been preferred to combine two plies by embossing them together. In this way, the rougher air-side surfaces of each ply may be joined to each other and thereby concealed within the sheet. However, producing two-ply products, even on state of the art CWP machines, lowers paper machine productivity by about 20% as compared to a one-ply product. In addition, there may be a substantial cost penalty involved in the production of two-ply products because the parent rolls of each ply are not always of the same length, and a break in either of the single plies forces the operation to be shut down until it can be remedied. Also, it is not normally economic to convert older CWP tissue machines to TAD. But even though through air drying has often been preferred for new machines, conventional wet pressing is not without its advantages as well. Water may normally be removed from a cellulosic web at lower energy cost by mechanical means such as by overall compaction than by drying using hot air.
What has been needed in the art is a method of making a premium quality single-ply absorbent paper using conventional wet pressing having a high bulk and excellent softness attributes. In this way advantages of each technology could be combined so older CWP machines can be used to produce high quality single ply absorbent paper products in the form of bathroom tissue and facial tissue at a cost which is far lower than that associated with producing two-ply absorbent paper.
Among the more significant barriers to the production of single-ply CWP absorbent paper have been the thinness and the extreme sidedness of single-ply webs. An absorbent product""s softness can be increased by lowering its strength, as it is known that softness and strength are inversely related. However, a product having very low strength will present difficulties in manufacturing and will be rejected by consumers as it will not hold up in use. Use of premium, low coarseness fibers, such as eucalyptus, and stratification of the furnish so that the premium softness fibers are on the outer layers of the tissue is another way of addressing the low softness of CWP products; however this solution is expensive to apply, both in terms of equipment and ongoing fiber costs. In any case, neither of these schemes addresses the problem of thinness of the web. TAD processes employing fiber stratification can produce a nice, soft, bulky sheet having adequate strength and good similarity of the surface texture on the front of the sheet as compared to the back. Having the same texture on front and back is considered to be quite desirable in these products or, more precisely, having differing texture is generally considered quite undesirable. Because of the deficiencies mentioned above, many single-ply CWP products currently found in the marketplace are typically low end products. These products often are considered deficient in thickness, softness, and exhibit excessive two sidedness. Accordingly, these products have had rather low consumer acceptance and are typically used in xe2x80x9caway from homexe2x80x9d applications in which the person buying the tissue is not the user.
We have found that we can produce a soft, high basis weight, high bulk, high strength CWP bathroom tissue, facial tissue, and napkins with low sidedness having a serpentine configuration by judicious combination of several techniques as described herein. Basically, these techniques fall into four categories: (a) providing a furnish to a web such that at least 20 percent by weight of the fibers in the web have a coarseness exceeding 23 mg/100 m; (b) at least about 20 percent by weight of the fibers in the web have a coarseness of less than about 12 mg/100 m; (c) the weight average coarseness to length ratio of the fibers in the web is less than about 8.5 mg/100 m/mm; and (d) optionally, the weight-weighted average fiber length is selected to be greater than about 1.75 mm. In addition, optionally, a controlled amount of temporary wet strength may be added along with a softener or debonder. By various combinations of these techniques as described, taught, and exemplified herein, it is possible to almost xe2x80x9cdial inxe2x80x9d for the absorbent paper the required degree of softness, bulk, and strength depending upon the desired goals. The use of softeners having a melting range of about 1xc2x0-40xc2x0 C. and being dispensable at a temperature of about 1xc2x0-100xc2x0 C. suitably 1xc2x0-40xc2x0 C. preferably 20xc2x0-25xc2x0 C. further improves the properties of the one-ply, high bulk, soft, absorbent paper product having a serpentine configuration.
The present invention is directed to a soft, strong in use, bulky single-ply absorbent paper product having a serpentine configuration and processes for the manufacture of such paper. More particularly, this invention is directed to a soft, strong-in-use, bulky, single-ply bathroom tissue, facial tissue, and napkin.
Paper is generally manufactured by suspending cellulosic fiber of appropriate geometric dimensions in an aqueous medium and then removing most of the liquid. The paper derives some of its structural integrity from the mechanical arrangement of the cellulosic fibers in the web, but most by far of the paper""s strength is derived from hydrogen bonding which links the cellulosic fibers to one another. With paper intended for use as bathroom tissue, the degree of strength imparted by this inter-fiber bonding, while necessary to the utility of the product, can result in a lack of perceived softness that is inimical to consumer acceptance. One common method of increasing the perceived softness of bathroom tissue is to crepe the paper. Creping is generally effected by fixing the cellulosic web to a Yankee drum thermal drying means with an adhesive/release agent combination and then scraping the web off the Yankee by means of a creping blade. Creping, by breaking a significant number of interfiber bonds adds to and increases the perceived softness of resulting tissue product.
Another method of increasing a web""s softness is through the addition of chemical softening and debonding agents. Compounds such as quaternary amines that function as debonding agents are often incorporated into the paper web. These cationic quaternary amines can be added to the initial fibrous slurry from which the paper web is subsequently made. Alternatively, the chemical debonding agent may be sprayed onto the cellulosic web after it is formed but before it is dried.
The most pertinent prior art patents will be discussed but, in our view, none of them can be fairly said to apply to the one-ply, absorbent paper of this invention which exhibits high bulk, soft and strong attributes. U.S. Pat. Nos. 5,405,499; 5,585,685; and 5,679,218 are irrelevant to our invention since, by the processes disclosed in those applications, the high coarseness fibers necessary to practice our invention are excluded.
Other prior references include Williams, U.S. Pat. No. 4,247,362, which is related to non delignified softwood and specially treated defibered hardwood; the majority of fibers in the sheet are softwood; Cochrane, et al., U.S. Pat. No. 4,874,465 discloses a sliced (lengthwise) fiber; Reeves, et al., U.S. Pat. No. 5,320,710 discloses hesperaloe fiber; Back, et al., U.S. Pat. No. 5,582,681 discloses newsprint printed with oil-containing ink wherein the pulp is treated with enzymes. All of these patents require the use of unique specialized fiber or a non-conventional stock preparation method, in contrast to the current invention which utilizes conventional paper making fibers prepared by standard pulping and stock preparation methods. Representative layered or stratified paper products in contrast to the present invention which comprises a single (homogenous) layer include Dunning et al, U.S. Pat. No. 4,166,001; Carstens, U.S. Pat. No. 4,300,981; Awofeso, et al., U.S. Pat. No. 5,087,324; and Awofeso, et al., U.S. Pat. No. 5,164,045. From the foregoing discussion of the prior art, it is clear that none of the references relate to one-ply, absorbent papers produced by (a) providing a furnish to a web such that at least 20 percent by weight of the fibers in the web have a coarseness exceeding 23 mg/100 m; (b) at least about 20 percent by weight of the fibers in the web have a coarseness of less than about 12 mg/100 m; (c) the weight average coarseness to length ratio of the fibers in the web is less than about 8.5 mg/100 m/mm; and (d) optionally, the weight-weighted average fiber length is selected to be greater than about 1.75 mm.
In addition, the foregoing prior art references do not disclose or suggest a high-softness, bulky, strong one-ply absorbent paper product in the form of a bathroom tissue and facial tissue having serpentine configuration and having a total specific tensile strength of no more than 200 grams per three inches per pound per 3000 square foot ream, a cross direction wet tensile strength of at least 2.75 grams per three inches per pound per 3000 square foot ream, a specific geometric mean tensile stiffness of 0.5 to 3.2 grams per inch per percent strain per pound per 3,000 square foot ream, a GM friction deviation of no more than 0.25 which are produced when, optionally, temporary wet strength agents and softeners/debonders are added to the web or furnish after the fiber selection has been made wherein (a) at least 20 percent by weight of the fibers in the web have a coarseness exceeding 23 mg/100 m; (b) at least about 20 percent by weight of the fibers in the web have a coarseness of less than about 12 mg/100 m; (c) the weight average coarseness to length ratio of the fibers in the web is less than about 8.5 mg/100 m/mm; and (d) optionally, the weight-weighted average fiber length is greater than about 1.75 mm.
The novel premium quality high-softness, bulky, single-ply absorbent paper product having a serpentine configuration is advantageously obtained by using a combination of five processing steps.
We have found that we can produce a soft, high basis weight, high bulk, high strength CWP bathroom tissue, facial tissue, and napkins with low sidedness having a serpentine configuration by judicious combination of several techniques as described herein. Basically, these techniques fall into four categories: (a) providing furnish to a web such that at least 20 percent by weight of the fibers in the web have a coarseness exceeding 23 mg/100 m; (b) at least about 20 percent by weight of the fibers in the web have a coarseness of less than about 12 mg/100 m; (c) the weight average coarseness to length ratio of the fibers in the web is less than about 8.5 mg/100 m/mm; and (d) optionally, the weight-weighted average fiber length is selected to be greater than about 1.75 mm. In addition, optionally, a controlled amount of temporary wet strength agent may be added along with a softener/debonder. By various combinations of these techniques as described, taught, and exemplified herein, it is possible to almost xe2x80x9cdial inxe2x80x9d for the absorbent paper the required degree of softness, bulk, and strength depending upon the desired goals. The use of softeners having a melting range of about 1xc2x0-40xc2x0 C. and being dispensable at a temperature of about 1xc2x0-100xc2x0 C., suitably 1xc2x0-40xc2x0 C., preferably 20xc2x0-25xc2x0 C., further improves the properties of the one-ply, high bulk, soft, absorbent paper product having a serpentine configuration.
One-ply CWP absorbent paper products such as bathroom tissue and facial tissue are formed from a furnish that includes high bulk fibers such as Southern pine or Douglas fir and low coarseness fibers such as Northern hardwoods and eucalyptus. Prior art has recommended that, for maximum softness, low coarseness Northern softwoods such as spruce or fir be used in the furnish. However, one-ply CWP tissues made ply from low-coarseness hardwoods and softwoods exclusively can have low thickness. We have discovered that blends of high bulk and low coarseness fibers had good softness and thickness attributes. In our process the high bulk fibers are included in sufficient quantity to result in good internal sheet delamination at the crepe blade. This delamination has a significant impact in producing a bathroom tissue or a facial tissue with good perceived thickness. Suitably, the fibers are blended in proportions such that the fiber coarseness/fiber length ratio of the blended fibers is controlled to a relatively low value. Our one-ply, absorbent paper products are suitably manufactured as a homogenous structure. Specifically, the furnish comprises (a) at least 20 percent by weight of the fibers in the web having a coarseness exceeding 23 mg/100 m; (b) at least about 20 percent by weight of the fibers in the web having a coarseness of less than about 12 mg/100 m; (c) the weight average coarseness to length ratio of the fibers in the web is less than about 8.5 mg/100 m/mm; and (d) optionally, the weight-weighted average fiber length is selected to be greater than about 1.75 mm. In addition, optionally, a controlled amount of temporary wet strength agent may be added along with a softener/debonder.
Further advantages of the invention will be set forth in part in the description which follows. The advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing advantages and in accordance with the purpose of the invention as embodied and broadly described herein, there is disclosed:
A method of making a high-softness, high strength, high bulk, single-ply absorbent paper product having a serpentine configuration. This paper product is suitably used in the form of a bathroom tissue or facial tissue. The absorbent paper product is prepared by:
(a) providing a fibrous pulp of papermaking fibers wherein the cellulosic fibers incorporated in the furnish for the web such that: (i) at least 20 percent by weight of the fibers in the web have a coarseness exceeding 23 mg/100 m, (ii) at least about 20 percent by weight of the fibers in the web have a coarseness of less than about 12 mg/100 mm, (iii) the weight average coarseness to length ratio of the fibers in the web is less than about 8.5 mg/100 m/mm, and (iv) optionally, the weight-weighted average fiber length is selected to be greater than about 1.75 mm;
(b) forming a nascent web from said pulp, wherein said web has a basis weight of at least about 12.5 lbs./3000 sq. ft. ream;
(c) optionally including in said web at least about 3 lbs./ton of a temporary wet strength agent and up to 10 lbs./ton of a nitrogen containing softener; optionally a cationic nitrogen containing softener; dispersible in water at a temperature of about 1xc2x0-100xc2x0 C. suitably 1xc2x0-40xc2x0 C. advantageously 20xc2x0-25xc2x0 C., advantageously the softener has a melting point below 40xc2x0 C.;
(d) dewatering said web;
(e) adhering said web to a Yankee dryer;
(f) creping said web from said Yankee dryer optionally using a creping angle of less than 85 degrees, wherein the relative speeds between said Yankee dryer and the take-up reel is controlled to produce a final product MD stretch of at least about 15%;
(g) optionally calendering said web;
(h) optionally embossing said web; and
(i) forming a single-ply web wherein steps (a)-(f) and optionally steps (g) and (h) are controlled to result in a single-ply absorbent paper product in the form of a bathroom tissue or facial tissue having a serpentine configuration, high bulk, and a total specific tensile strength of no more than 200 grams per three inches per pound per 3,000 square foot ream, suitably no more than 150 grams per three inches per pound per 3,000 square foot ream, preferably no more than 75 grams per three inches per pound per 3,000 square foot ream, a cross direction wet tensile strength of at least 2.7 grams per three inches per pound per ream, a specific geometric ream tensile stiffness of between 0.5 and 3.2 grams per inch per percent strain per pound per 3,000 square foot ream, a GM friction deviation of no more than 0.25.
To summarize, at a total specific tensile strength of about 200 grams per 3 inches per pound per 3,000 square foot ream or less, the cross direction specific wet tensile strength is about 20 grams per pound per 3,000 square foot ream or higher, the ratio of MD tensile to CD tensile is between 1.25 and 2.75. The specific geometric mean tensile stiffness is 3.2 or less grams per inch per percent strain per pound per 3000 square foot ream. The friction deviation is less than 0.25. At a total specific tensile strength of about 150 grams per pound per 3 inches or less per 3000 square foot ream the cross direction specific wet tensile strength is about 15 grams or less per pound per 3000 square foot ream, the ratio of MD tensile to CD tensile is between 1.25 and 2.75. The specific geometric ream tensile stiffness is 2.4 or less grams per inch per percent strain per pound per 3000 square foot ream and the friction deviation is less than 0.25. When the bathroom tissue or facial tissue product exhibits a total specific tensile strength between 40 and 75 grams per 3 inches per pound per 3000 square foot ream, it has a cross direction specific wet tensile strength of between 2.75 and 7.5 grams per 3 inches per pound per 3000 square foot ream, and its specific geometric mean tensile stiffness is between 0.5 and 1.2 grams per inch per percent strain per pound per 3000 square foot ream and its friction deviation is less than 0.225.
In one embodiment of this invention, the one-ply, absorbent paper product may be embossed with a pattern that includes a first set of bosses which resemble stitches, hereinafter referred to as stitch-shaped bosses, and at least one second set of bosses which are referred to as signature bosses. Signature bosses may be made up of any emboss design and are often a design which is related by consumer perception to the particular manufacturer of the tissue.
In another aspect of the present invention, a paper product is embossed with a wavy lattice structure which forms polygonal cells. These polygonal cells may be diamonds, hexagons, octagons, or other readily recognizable shapes. In one preferred embodiment of the present invention, each cell is filled with a signature boss pattern. More preferably, the cells are alternatively filled with at least two different signature emboss patterns.
In another preferred embodiment, one of the signature emboss patterns is made up of concentrically arranged elements. These elements can include like elements for example, a large circle around a smaller circle, or differing elements, for example a larger circle around a smaller heart. In a most preferred embodiment of the present invention, at least one of the signature emboss patterns are concentrically arranged hearts as can be seen in FIG. 3. Again, in a most preferred embodiment, another signature emboss element is a flower.
The one-ply absorbent paper of this invention in the form of a bathroom tissue or facial tissue has higher softness, bulk, and strength parameters than prior art one-ply absorbent paper products and the embossed one-ply bathroom tissue product and the facial tissue product of the present invention has superior attributes than prior art one-ply embossed tissue products. The use of concentrically arranged emboss elements in one of the signature emboss patterns adds to the puffiness effects realized in the appearance of the paper product tissue. The puffiness associated with this arrangement is the result not only of appearance but also of an actual raising of the tissue upward aided by the bulky cellulosic fibers.
In another embodiment of the present invention, the tissue is embossed between two hard rolls each of which contain both micro male and female elements although some signature or macro elements can be present. The micro male elements of one emboss roll are engaged or mated with the female elements of another mirror image emboss roll as can be seen in FIG. 7. These emboss rolls can be made of materials such as steel or very hard rubber. In this process, the base sheet is only compressed between the sidewalls of the male and female elements. Therefore, base sheet thickness is preserved and bulk perception of a one-ply product is much improved. Also, the density and texture of the pattern improves bulk perception. This mated process and pattern also creates a softer tissue because the top of the tissue protrusions remain soft and uncompressed.
The male elements of the emboss pattern are non-discrete, that is, they are not completely surrounded by flat land area. There are approximately an equal number of male and female elements on each emboss roll. This increases the perceived bulk of the product and makes both sides of the emboss tissue symmetrical and equally pleasing to the touch.
Another advantage of the mated embossed embodiment of the present invention is the type of textured surface that is created. This texture provides for better cleansing of the skin than a typically embossed CWP one-ply tissue which is very smooth in the unembossed areas. The surface of the CWP product of the present invention is better than that of a typical through-air-dried (TAD) product in that it has texture but more uniformly bonded fibers. Therefore, the fibers on the surface of the tissue do not pill or ball up, especially when the tissue becomes wet. In contrast, there are significant portions of the typical textured TAD tissue surface where fibers are weakly bonded. These fibers tend to pill when the tissue becomes wet, even when a significant amount of wet strength has been added to the fibers.
A preferred emboss pattern for the present invention is shown in FIGS. 4A-1, 4A-2, 4A-3 and 4B. It contains diamond shaped male, female and mid-plane elements which all have a preferred width of 0.023 inches. The width is preferably between about 0.005 inches and about 0.070 inches, more preferably between about 0.015 inches and about 0.045 inches, most preferably between about 0.025 inches and about 0.035 inches. The shape of the elements can be selected as circles, squares or other easily understood shapes. When a micro and macro pattern are used, the distance between the end of the macroelements and the start of the microelements is preferably between about 0.007 inches and about 1 inch, more preferably between about 0.005 and about 0.045, and most preferably between about 0.010 and about 0.035. The height of the male elements above the mid-plane is preferably about 0.0155 inches and the depth of the female elements is preferably about 0.0155 inches. The angle of the sidewalls of the elements is preferably between about 10 and about 30 degrees, more preferably between about 18 and about 23 degrees, most preferably about 21 degrees. In a most preferred embodiment, the elements are about 50% male and about 50% female.
Patterns such as those shown in FIGS. 4A-1, 4A-2, 4A-3 and 4B can be combined with one or more signature emboss pattern to create products of the present invention. Signature bosses are made up of any emboss design and are often a design which is related by consumer perception to the particular manufacturer of the tissue.
More preferred emboss patterns for the present invention are shown in FIGS. 5A-1, 5A-2, 5A-3, 5B-1, 5B-2 and 5B-3. These patterns are exact mirror images of one another. These emboss patterns combine the diamond micro pattern in FIGS. 4A-1, 4A-2, 4A-3 and 4B with a large, signature or xe2x80x9cmacroxe2x80x9d pattern. This combination pattern provides aesthetic appeal from the macro pattern as well as the improvement in perceived bulk and texture created by the micro pattern. The macro portion of the pattern is mated so that it does not reduce softness by increasing the friction on the back side of the sheet. In addition to providing improved aesthetics, this pattern minimizes nesting (the complete overlap of embossing elements) and improves roll structure by increasing the repeat length for the pattern from 0.0925 inches to 5.0892 inches.
The design of the macroelements in the more preferred emboss pattern preserves strength of the tissue. This is done by starting the base of the male macroelements at the mid-plane of the microelements as shown in FIGS. 5B-1, 5B-2 and 5B-3. The female macroelements are started at the mid-plane of the microelements as shown in FIGS. 5A-1, 5A-2 and 5A-3. This reduces the stretching of the sheet from the mid-plane by 50%. However, because the macroelements are still 31 mils in height in depth, they still provide a crisp, clearly defined pattern.
The more preferred emboss pattern has the bases of male microelements and the opening of female microelements kept at least 0.014 inches away from the base of male macroelements or openings of female macroelements. This prevents the emboss rolls from plugging with tissue.
It is also possible to put some of the male macroelements going one direction and the rest of them going the other direction. This may further reduce any sidedness in the product. FIGS. 5c and 5d show the actual size of the preferred patterns.